Sometimes readers need to be reminded that just because a character has been around in Marvel stories for 40 or 50 years, doesn't mean that the characters have 40-50 years worth of 'real time' history and memories. The passage of time in Marvel comics is fuzzy. There's 'now' and there's 'previously' and both those time frames shift and compress and blur together constantly. So 'previously' Wanda had a lower level of power and was told she was a mutant, but 'now' she is a nexus being who is tapped into a cosmic-level magical energy source. So far as Wanda herself is concerned, everything in the of the last 50 years of real world storytelling time feels to her like maybe a few months to a couple of years. Time does not pass for these characters at the same rate that it passes for the readers. So Wanda isn't a 'slow learner' at all just because she transformed from one level of power to another over the last several decades of real world time. To her, it probably all feels like a fuzzy few months.